Action Points

Note that this population-based Swedish study found that ankylosing spondylitis was associated with an increased risk of death compared with the general population.

Increased mortality rates were similar to those seen among individuals with rheumatoid arthritis.

Mortality is increased for patients with ankylosing spondylitis, and to a similar degree as has been seen in rheumatoid arthritis, a Swedish nationwide, population-based study found.

Compared with the general population, the age- and sex-adjusted hazard ratio for all-cause mortality among individuals with ankylosing spondylitis was 1.60 (95% CI 1.44-1.77), according to Sofia Exarchou, MD, of Lund University in Malmo, and colleagues.

And the risk was higher for both men (HR 1.53, 95% CI 1.36-1.72) and women (HR 1.83, 95% CI 1.50-2.22), the researchers reported online in Annals of the Rheumatic Diseases.

Increases in mortality have consistently been shown for some diseases characterized by chronic inflammation, such as psoriasis and rheumatoid arthritis, but few studies have addressed this in ankylosing spondylitis. The studies that have been done, which were small and not population-based, generally found standardized mortality ratios of 1.33 to 1.80, but little is known about potential risk factors in this patient population.

"The relative mortality risk in ankylosing spondylitis that we observed was similar to that reported in rheumatoid arthritis, where the mean standardized mortality ratios of non-inception cohorts were 1.73," Exarchou and colleagues wrote.

To address the uncertainty about mortality and risk factors in ankylosing spondylitis, the researchers analyzed data from the Swedish National Patient Register, identifying 8,600 cases and 40,460 matched controls. Follow-up began in 2006 and continued through 2012.

Two-thirds of the cases were men, and mean age at the time of diagnosis was 42. About one-third had more than 12 years of education.

During follow-up, 496 patients with ankylosing spondylitis died, as did 1,533 controls, for crude mortality rates of 9.5 per 1,000 and 5.6 per 1,000 person-years, respectively.

Mortality rates were elevated across age groups for both sexes, and incidence rate ratios were 1.65 (95% CI 1.47-1.86) for men, 1.89 (95% CI 1.55-2.29) for women, and 1.71 (95% CI 1.55-1.90) overall.

The most common cause of death among cases was cardiovascular disease, at 34.7%, compared with 30.6% for controls.

Older age and male sex were associated with greater mortality, as were these other predictors:

Cardiovascular disease, HR 1.99 (95% CI 1.58-2.49)

Diabetes, HR 1.92 (95% CI 1.51-2.45)

Chronic pulmonary disease, HR 3.03 (95% CI 2.27-4.04)

Malignancy, HR 1.67 (95% CI 1.32-2.12)

Infections, HR 2.01 (95% CI 1.68-2.34)

A history of hip replacement surgery, which may reflect more severe disease, also was predictive (HR 1.65, 95% CI 1.29-2.12), while having had more than 12 years of education was associated with a lower mortality risk (HR 0.67, 95% CI 0.53-0.85), as has been seen in other conditions such as rheumatoid arthritis.

The finding that comorbidities such as cardiovascular disease were predictors of mortality was expected, "given the strong impact of these comorbidities on mortality in the general population," according to the authors.

"Since the present analyses were not based on an inception cohort, it was not possible to determine clearly whether this observation can be explained by a shared etiology between ankylosing spondylitis and cardiovascular disease (or other comorbidities), or whether general comorbidities represent path variables that are partially caused by ankylosing spondylitis, or whether the observation reflects detection bias," they noted.

Potential limitations of the study included diagnostic misclassification and selection bias, and the limited clinical and lifestyle information available in the national registers.

"Further studies are thus warranted to disentangle the effects of disease severity, comorbidities, and medication on mortality risk," the researchers concluded.

The study was funded by the Oak Foundation, the Swedish Rheumatism Association, and Lund University.